Copper base alloys and the method of treating the same to improve their machinability



M y 1966 H. BURG HOFF ETAL 3,253,910

\ COPPER BASE ALLOYS AND THE METHOD OF TREATING THE SAME To IMPROVETHEIR MACHINABILITY 5 Sheets-Sheet 1 Filed Au 31, 1964 Fig. 1Microotructure of typical showing Type 1 inclusion. Polished,

unetched. (X300) (Inclusion positioned between diamond-shaped locatingmarks) Fig. 3 Microstructure of typical commercial free-cutting brassrod showing Type 1 131cl1(1sion. Polished,

unetched. X300 Inclusion positioned between diamond-shaped locatingmarks) DAVID MENDS INVENTORS May 31, 1966 Filed Aug. 51. 1964 H.BURGHOFF ETAL 3,253,910 COPPER BASE. ALLOYS AND THE METHOD OF TREATINGTHE SAME TO IMPROVE THEIR MACHINABILITY 5 Sheets-Sheet 2 Fig. 4 I MicroSpecimen of Type 1 inclusion. Polished, unetched.

Fig. 5 Micro Specimen of e 1 (x1000) m inclusions. Polished unetched.(x1000) Fig. 6 Micro Specimen of Type 1 (lower right) and Type 2 (upperleft) inclusions. Polished, unetched. (X1000) Fig. 7 Micro Specimen ofType 2 inclusions. Polished, unetched. (x1000) Fig. 8 Micro Specimen ofType 2 inclusion. Polished, unetched.

HENRI L. HIRGHOFF F. GERAID PARKER DAVID MENIB INVENTORS y 1, 1966 H.BURGHOFF ETAL 3,253,910

COPPER BASE ALLOYS AND THE METHOD OF TREATING THE SAME TO IMPROVE THEIRMACHINABILITY Filed Aug. 31 1964 5 Sheets-Sheet 5 7- Tool Life vs.Silica Inclusions /mm m 5 5- O f Standard Free-Cutting Brass Rod(SilicoFree) E, Fl 6 9 2 2 o o o o L 1 2 4 6 8 l0 l2 Silica inclusions /mm 7Tool Life vs. 6- Zinc Sulfide Inclusions /mm m F I (5 IO 0 I l l I l I 0IO 3O 5 7Q Zinc Sulfide Inclusions/mm EM L. manom- F. GERALD PARKERDAVID MENIB IN VEN TORS United States Patent 3,253,910 COPPER BASEALLUYS AND THE METHOD OF TREATING THE SAME TO IMPROVE THEIRMACHINABKLITY Henry L. Burgholf and Frederick GeraldParker, Waterbury,and David Mends, Newtown, Conn., assignors to Chase Brass and Copper Co.Incorporated Filed Aug. 31, 1964, Ser. No. 393,368 15 Claims. (Cl.75135) This application is a continuation-in-part of the earlierapplication of Henry L. Burghoif and Frederick Gerald Parker, UnitedStates Serial No. 119,009, filed May 8, 1961, now United States Patent3,15 8,470, granted November 24, 1964.

This invention is concerned with improvement in the machinability ofcopper-base alloys, and moreparticularly in leaded brasses, of the typeused in large quantity for producing machined parts. The invention isespecially directed to copper alloys for producing rod from which suchparts, commonly characterized as screw machine parts, are fabricated byrepetitive operations on an automatic machine. In such operations theresistance to wear of cutting tools which results from high ratesof-sustained, repetitive machining operations, is a vitally importantfactor in achieving maximum'machine production while maintainingdimensional tolerance and surface finish requirements in the partsproduced. We have found that the machinability of these copper-basealloys is remarkably affected by certain hitherto unsuspectedcharacteristics of these alloys. As a result of this, we have foundmeans whereby deleterious variations in machinability may be minimizedand new heights of machinability obtained.

Leaded brasses ofnumerous compositions have long been used in industrybecause of the case with which they canbe machined. The lead which ispresent in such alloys imparts the characteristic of free machining. Inwrought alloys, lead may be present to as much as about 4%. The higherthe lead content within this range, the higher or better is themachinability. Alloys of intermediate lead content represent acompromise between easy machinability on the one hand, and other typesof workability on the other hand, such as 'flanging, knurling, threadrolling, forming and drawing.

An alloy known generally as free-cutting brass, having a nominalcomposition of 60-63% copper, 2.5%- 3.7% lead, the remainder zinc exceptfor the usual incidental impurities, is the alloy most frequently usedin making arts on automatic screw machines. This composition rangerepresents a combination of high machinability and desirable mechanicalproperties. Despite its long record of being one of the most machinableof alloys, there have been complaints with regard to the variability ofits performance, inconsistent and premature wearingof cutting tools,consequential damage to tools and interruption of operations in ordertore-grind the cutting edge or to replace the tools. Sometimes it isnecessary to reduce the speed of machining in order to extend tool lifeor to be able to make a satisfactory part.

It has been suggested from time to time that hard inclusions, suchas'particles of undissolved steel or iron in the brass might beresponsible for the poor performance on such occasions, and diligentsearches have been made and samples of such brass carefully investigatedfor such inclusions. It is a known fact that foreign material such asiron or steel is often included in the metal scrap which conventionallyis included in the starting charge in the melting and casting of thealloy. On rare occasions such metallic inclusions have indeed been foundin the finished product. Much more often, however, no rationalexplanation of the untoward behavior has been found and gen- "ice erallythe incidents 'have been passed off as operational inefiiciency,poormachine set-up or personal idiosyncrasies of the machine operator.

In order to arrive at a better understanding of the machiningcharacteristics of brass, we have undertaken a program to evaluatefactors important to matching, including: composition with respect toactual content of copper, lead and zinc, the basic ingredients;impurities which may be brought in from various sources and includingelements such as iron, tin, aluminum, silicon, chromium; also themicrostructure of the alloy; temper of the rod; surface finish andcleanliness of the rod; angles and feeds of tools; and speed of rotationof the rod.

With the foregoing factors in mind we have used'an automatic form andcutoff machine capable of unusually high maximum rotational speeds forthe determination of the machinability behavior of free-cutting brassrod heretofore; generally available from various commercial sources.A'variety 'of cutting operations including forming, drilling, reaming,balance turning and cut-ofi" have been examined and a statisticalanalysis has been made of variation in diameter of successive workpieces produced by this machine from these materials and its relation tothe "machine capability. Consistent and rational results have beenobtained in this investigation, and they are found to substantiategeneral experience in commercial screw machine shops. Thus, forcommercial free-cutting brass generally available heretofore, a 4-hourlife has been established as the normal best expectancy for a high speedsteel form tool, before re-sharpening, when operating at a spindle speedof 12,000 r.p.m. and a tool feed of 0.002 inch per revolution on /z"diameter rod to produce a given work piece. It has been found, however,that the machining characteristics of different lots of free-cuttingbrass rod may vary widely, and in fact a lot of rod used in one test cangive vastly different machinability results from another'lot of rod,nominally of'the same composition and production history, subjected tothe same "control test. Forexample, instead of obtaining-the normallybest expected 4-hour tool life, a life of only 2 hours, or even less, isall that is obtained with certain lots of rod and, furthermore, thetools in these instances are worn as though they have been ground withan abrasive.

Examination of the microstructure of rod giving such inferior results,in order to determine if any deleterious inclusions were present, wasfruitless at first. This is not surprising in view of the difiiculty of'finding minute foreign particles amidst the myriad of discrete particlesof 'lead which are present characteristically in the alloy. Reference toFIG. 1 of the drawings will bear this out, wherein the microstructure oftypical free-cutting brass, free of any beta phase, is shown in thephotomicrograph. However, after persistently examining carefullyprepared samples at a high magnification, on the order of1,000-diameters, under the microscope, we have discovered that thereare, indeed, inclusions present in conventional free-cutting brass thatcannot be rationalized from knowledge of the ordinary chemical analysesof composition of the alloy. These inclusions generally range in theirlongest dimension from something less than 1 micron to as much as 50microns. Application of a Bergsman microhardness tester to these fineparticles indicates that they are of two general levels of hardness. Thefirst, originally classified as type 1 and now believed to'beessentially silica, SiO has a hardness about ten times as greatas thatof the brass itself. The other type, type 2 and now believed to beessentially zinc sulfide, ZnS, has about two to three times the hardnessof brass itself. FIGS. 28 of the drawings illustrate various forms ofthese inclusions at magnifications of 300 and l000 Positivecompositional identification of these two types of particles isextremely difficult but we believe that the characterization of them assilica and zinc sulfide is now reasonably accurate and assured. Forconvenience, therefore, in the discussion which follows they will bereferred to by these terms.

Upon arriving at the foregoing discovery, in carrying out machiningtests on numerous lots of rod obtained from a wide variety of commercialsources, we have found that tool life is definitely related to bothtypes of inclusions. Where there is substantially no silica present andthe observed average count of zinc sulfide inclusions is on the order of20 to 40 per square millimeter, the tool life found is the best expectedfor normal conventional rod. Our studies clearly show that where anysilica particles are present, form tool life is adversely affected. Whenon the average as few as two of these inclusions per square millimeterof metal surface as examined under a microscope are observed, the formtool life is drastically reduced from the best life expected in thecutting of normal conventional rod. Where the free-cutting brass containan abserved average of about 70 inclusions of zinc sulfide per squaremillimeter of examined surface, but with substantially no silicapresent, the tool life is also reduced appreciably below the bestexpected life. But Where there are substantially no inclusions, eitherof silica or of zinc sulfide, a remarkable increase in tool life isfound amounting to from 2 to 5 times the normal best expected life forconventional free-cutting brass.

For the purposes of this discussion and in the appended claims, theexpressions substantially complete elimination of inclusions, orsubstantially complete absence of inclusions are employed to mean thefollowing: In the case of silica, these expressions denote that not morethan one such inclusion, and preferably none at all, is observed underthe conditions hereinafter explained per square millimeter ofrepresentative alloy surface; and in the case of zinc sulfide, not morethan ten and preferably less than five inclusions are observed persquare millimeter of alloy surface.-

The presence of sulfur in copper alloys has in the past,

never been regarded as harmful to machinability. In-

deed, it is customary to add as. much as 0.25% sulfur to copper to forma commercial alloy whose distinguishing characteristic is improvedmachinability with respect to pure copper itslef. In copper, this sulfurexists as discrete particles of copper sulfide. Similarly, sulfur isadded to certain steels for the purpose of improving machinability. Ourfinding that sulfur in brass is detrimental to its machinability istherefore most unexpected and contrary to reasonable anticipation and isof very significant commercial importance.

Inclusions of one or both types described above have been found in somefree-cutting brass rod of all of the various sources of supply tested,indicating their widespread and uncontrolled occurrence in commercialmaterial. Visual identification of the inclusions can be made provided amagnification of at least 1000 is employed. Using this order ofmagnificatiomthe silica and zinc sulfide inclusions can be visuallyidentified by their shape, color, location and size. In the case of thesilica inclusions, the shape is usually oblong or irregular, ranging, asindicated above, in maximum dimension from about 1 micron to 50 microns.The silica inclusions are dark blue-gray in color and stand out inrelief when polished. Commonly there are imperfections in the inclusionsand their surface is pitted. The silica inclusions are never sphericalwhich helps to distinguish them from the zinc sulfide inclusions.

The latter are generally spherical or geometrical in shape and sometimeshave a tail or irregularity attached to the nodule. These sulfideinclusions polish flat and range in color from light to dark gray, oftenbeing mottled in appearance. Their distribution is apparently quiterandom throughout the cross-section of the rod and they range from about1 to 5 microns in size.

Microhardness tests on the inclusions themselves vary from around 1,000to 1,600 Knopp hardness numbers (KI-IN), for the silica, while the zincsulfide inclusions range between 180 to 380 KHN.

Wherever examination of the alloy reveals an inclusion count which, onthe average, indicates the presence of 1 silica inclusion per squaremillimeter of surface examined, the life of the cutting edge of the toolis reduced by about one-fourth as compared with the life of that toolwhen cutting silica-free rod. Thus it is apparent that silica inclusionsin the rod have an extremely important effect on tool life. The effectof silica inclusions on tool life when forming or machining free-cuttingbrass is illustrated graphically in FIG. 9 of the accompanying drawings.The data plotted on this chart was obtained from machining varioussamples of /2 diameter free-cutting brass rod using a molybdenum highspeed steel form tool having a back rake angle of +2. A chemicallubricant, diluted 1:25 with Water, was applied during the machiningoperation and the cutting speed was 1570 surface feet per minute at afeed rate of 0.002 inch per revolution.

The effect of zinc sulfide inclusions on tool life, in the absence ofsilica, is shown on the graph of FIG. 10 from which it is noted thattool life increases as the zinc sulfide count decreases. Zinc sulfideinclusions, however, are not as detrimental to tool life as are thesilica inclusions, unless the sulfide count is greater than about 70 toinclusions per millimeter. Quite commonly the zinc sulfide count incommercial free-cutting brass is between 20 to 40 per square millimeter.

Some appreciation of the difiiculty of identifying the deleterious zincsulfide inclusions in the brass matrix already peppered with leadinclusions can be gained when it is considered that many of theseapproach 1 micron in size.

In spite of the smallness of these sulfide inclusions, however, aslittle as 0.00*1% sulfur in the brass can produce on the order 5 10particles of 1 micron size per cubic inch of metal, which explains insome measure their effect on tool life.

In order to determine the inclusion count, this is made with amicroscope using a magnification of l000 over a sufficient number ofdifierent fields to provide a representative count for a total examinedarea equivalent to one square millimeter. Fields near the outsidesurface of the material are included in order, to make sure that silicainclusions, if present, will be found.

Having thus determined the cause or reason 'for the difficulties andvariable results in machinability of the copper base alloys, the nextstep is to provide a cure. We have found that the foregoing zinc sulfideinclusions and, surprisingly, the silica inclusions also can beeliminated from the alloy by the addition of a suitable reagent metal tothe melt shortly before casting. Magnesium is particularly effective butother reagent metals can also remove the undesirable inclusions frombrass either partially or wholly. These include sodium and certain rareearth mixtures which are rich in lanthanum and/or cerium. Manganeseappears definitely not to be effective.

In the case of magnesium, useful improvements in clearing themicrostructure and in obtaining better machin bility are obtained withfrom about 0.01% to as high as 0.23% residual magnesium in thefree-cutting brass. Residual magnesium of 0.35% produces hot shortnessin extrusion and cold shortness in cold drawing of rod of the alloy,both operations being conventional in commercial production. The upperlimit of retained magnesium practical in the brass thus appears to be inthe neighborhood of 0.3%. Optimum content, both from machina bility aswell as economic consideration, is on the order of 0.02% to 0.18%magnesium.

The effect of the magnesium appears to be synergistic, for tool lifewith some magnesium-containing material is far greater than withnon-magnesium treated material having low or no undesirable inclusions.

The beneficial effect of magnesium is set forth in the accompanyingTable I which shows form tool life for a standard test as great as 20hours for one magnesium-bearing rod, pronounced improvement overcommercial inclusion-containing material for all magnesium contents inthe useful range.

The improvement from the use of magnesium is obtained despite the factthat it, too, produces discrete particles of a phase which is alsoharder by 2 to 3 times than the brass in which it occurs. Such a phasewill be found with magnesium contents ofabout 0.06% and higher.

TABLE I.-EFFECT OF MAGNESIUM IN BRASS ON TOOL LIFE DIAMETER FREE-CUTTINGBRASS ROD [Nominal composition: 61% Cu, 3.2% Pb, bal. Zn]

Inclusions/mm. Rod. No. Magnesium, Tool lite,

percent hours Silica Zinc sulfide 1 1. 2 9 2 2. 0 8 66 3.. 1.9 19 4..2.0 4 38 5 3. 2 0 80 6 4. 0 0 56 7-. 3, 1 0 40 8.. 3. 0 0 45 9-. 3. 8 041 10 3.0 0 40 11 4. 4 0 38 12. 4.6 0 31 13 3. 1 0 28 14 4. 0 0 25 15.5. 7 0 O 1ti 20. 8 0 0 17 13. 3 0 0 18... 17. 1 0 0 19 1 17. 0 0 0 20.0. 080 9. 3 0 0 2L 0. 11 10. 1 0 0 22 0.16 12. 2 0 0 23... 0. 17 10.4 00 24 0. l8 7. 8 0 0 25 0. 23 5. 5 0 0 io HEXAGONAL FREE-CUTTING BRASSROD [Same nominal composition as above] %4 DIAMETER LEADED FLANGINGBRASS ROD [Nominal composition: 62.5% Cu, 2% Pl), bal. Zn]

1 Test discontinued; tool still in good condition.

Production of magnesium-containing copper alloy may be accomplished inseveral different Ways. In the first of a series of heats of commercialsize, the preparation of a nominal 0.2% magnesium-bearing copper alloywas accomplished from a charge consisting entirely of free-cutting brassscrap. This was charged into a furnace and immediately after melt-down,with the melt relatively cool, the dross was raked off the melt andmagnesium was added in the form of an 80% Cu% Mg master alloy. Themaster alloy was introduced by thrusting it beneath the surface with aladle, with the furnace power on. When the furnace reached pouringtemperature, power was turned off and the melt allowed to stand for fiveminutes. The melt was then skimmed and poured into a mold.

Mechanical properties, assay results, inclusion counts and machinabilitydata .for a typical Melt A prepared in this way are shown in theaccompanying Tables H, III and IV.

A second series of ingots was cast from charges consisting mainly ofscrap, including small amounts of chips. Magnesium was again added asthe copper-magnesium master alloy, and the metal allowed to stand for 2minutes 6 with the furnace off before pouring. The results of this aretypified by the data given for Melt B in the accompanying Tables II, IIIand IV.

Ingots containing no magnesium addition were also poured for comparisonpurposes, and the properties of a representative ingot from this groupare shown in the accompanying tables as Melt C.

A further series of ingots was produced with contents up to 0.35%magnesium. Hot extruded and coiled rod with 0.35% Mg was found tocontain intercrystalline cracks. It also proved impossible to point theends of the rods without further cracking them. Examination of themicrostructure of this rod showed lead and both alpha and beta phases tobe present, together with particles produced by the magnesium, mainly inthe form of an intercrystallin'e network. This was probably the cause ofthe cracking and thus indicates definitely an upper limit for themagnesium content.

The addition of magnesium to the melt may be accomplished by the use ofunalloyed magnesium metal as well as in the form of a mastercopper-magnesium alloy specifically mentioned in the foregoing examples.

The presence of magnesium in the melt exerts a marked effect on thetendency of zinc to burn during pouring. Thus it is observed that thestream of metal becomes covered with a thin skin of adherent oxide whichprotects the zinc from burning. The magnesium additions, although theymay cause the formation of more dross than usual, tend to decrease zincstack losses which is definitely a favorable factor.

From the results shown in Tables II, III and IV, it is seen that thereis no significant difference in mechanical properties, grain size orbeta content as a result of magnesium additions. On the other hand,there is a marked increase in tool life in the magnesium-bearingbrasses.

TABLE II.MECHANIOAL PROPERTIES Melt Properties Percent Mg (retained) Q0.17 0. 11 Tensile strength, p.s.i 61, 600 66, 300 66, 300 Yieldstrength, p.s.i. 43, 000 45, 500 42, 200 Percent elongation (2) 17 17Grain size 0. 030 0. 030 07 030 Hardness (Rockwell B):

Surfa 77 76 75 Mid-radiu 73 76 75 Centel 71 74 76 Percent beta ph 1 1 2TABLE IIL-ASSAY RESULTS (PERCENT) Melt Analysis TABLE IV.INCLUSIONCOUNTS AND TOOL LIFE Melt A i B i 0 Mg (percent). 0. 17 0. 11Inclusions/mm nominal lead content is on the order of 2%.

As previously mentioned we have found that reagent metal additions otherthan magnesium are useful for removing the undesirable inclusions.

In another case, the addition of approximately 0.14%

of misch metal (lanthanum-cerium alloy) is also beneficial. In all ofthese cases, the amount of reagent metal which is added should besubstantially less than that-of magnesium.

The brasses have long been recognized as among the cleanest alloysstructure-wise of all those commercially used, by virtue of their zinccontent and the purging action which this element itself exerts in themelting operation. The beneficial effect of additions of a reagent metalunder this circumstance is therefore a most unusual thing. 1

The invention is not limited to free-cutting brass but .is applicable tocommercial brasses, generally. In Table I an example of flanging brassis given, in which the And the same is applicable to low-leaded brasshaving a nominal composition of 66.5% copper-0.5% lead, balance zinc.The latter alloy shows inclusion counts typically of 4 silica, 30 zincsulfide inclusions per square millimeter. Nor is the invention limitedto leaded brasses as it may be applied to nominally lead-free alloys,such as cartridge brass (nominally 70% copper-30% zinc), and jewelrybronze (nominally 87.5% copper-12.5% zinc). The latter alloyparticularly is much used in the manufacture of slide fasteners and hasbeen found to produce large variation in the wear of the cut-off toolused in making the fastener elements. Typical inclusion counts for thisjewelry bronze show up to 5 silica and to 12 zinc sulfide particles persquare millimeter. The cartridge brass mentioned above shows, typically,silica counts of 6 to 7 and zinc sulfide counts as high as 75 onoccasion. Re-

moval of these inclusions from any of these alloys by the techniquedisclosed herein is beneficial.

TABLE V.-EFFECT OF SODIUM IN BRASS ON TOOL IIIFE V DIAMETER FREE-CUTTINGBRASS ROD [Nominal composition: 61% Cu, 3.2% Pb, bal. Zn]

What is claimed is:

1. A leaded brass alloy of improved machinability containing asinclusion-reducing reagent metal at least one member selected from thegroup consisting of sodium, lanthanum and cerium, the amount of saidreagent metal retained in the alloy being an effective amount sufficientto effect substantially complete elimination of silica inclusionscommonly present in the untreated alloy.

2. A leaded brass alloy as defined in claim 1, wherein the amount ofsaid reagent metal is an effective amount sufficient also to effectsubstantially complete elimination of zinc sulfide inclusions commonlypresent in the untreated alloy.

3. A leaded brass of improved machinability which has been treated toreduce silica and zinc sulfide inclusions commonly present in theuntreated metal, said treated brass containing as an inclusion-reducingreagent metal a member selected from the group consisting of sodium,lanthanum and cerium, in an effective amount sufficient to effectsubstantially complete elimination of such inclusions, the maximumamount of reagent metal retained in said brass being about 0.30% byweight.

4. A leaded brass of superior machinability which has been treated toreduce silica and zinc sulfide inclusions commonly present in theuntreated metal, said treated leaded brass containing an effectiveamount sufficient to effect substantially complete elimination of suchinclusions, up to 0.30% of an inclusion-reducing reagent metal selectedfrom the group consisting of sodium, lanthanum and cerium. I

5. A free-cutting brass of superior machinability having a'nominalanalysis of 60% to 63% copper, 2.5% to 3.7% lead, the remainder zincexcept for incidental impurities and an inclusion-reducing reagent metalin a retained small but effective amount, up to 0.30% by weight,sufficient to effect substantially complete elimination of silica andzinc sulfide inclusions commonly present inordinary free-cutting brassand being selected from the group consisting of sodium, lanthanum andcerium.

6. A free-cutting brass as defined in claim 5, wherein the reagent metalis sodium in amount of from about 0.000l% to 0.0005% by weight.

7. The method of treating leaded brass to reduce silica and zinc sulfideinclusions commonly present in the untreated metal in order to improvethe machinability thereof, which comprises introducing into the brassmelt at least one reagent metal selected from the group consisting ofsodium, lanthanum and cerium, in amount sufficient to provide in thecast alloy an effective amount sufiicient to effect substantiallycomplete elimination of such inclusions, up to 0.30% by weight of saidreagent metal.

8. The method as defined in claim 7, wherein thev amount of reagentmetal is sufficient to reduce silica and zinc sulfide inclusions in theuntreated alloy matrix to an average of not more than one silica and tenzinc sulfide inclusions per square millimeter of metal cross-sectionalsurface.

9. The method of treating free-cutting brass having a nominalcomposition of 6063% copper, 2.5%-3.7% lead, balance zinc, to improvethe machinability thereof, which comprises introducing into the alloymelt at least one reagent metal selected from the group consisting ofsodium, lanthanum and cerium, in an effective amount sufficient toeffect substantially complete elimination of silica and zinc sulfideinclusions commonly present in the untreated brass, and to provide inthe cast alloy not more than 0.30% of said reagent metal.

10. The method as defined in claim 9, wherein the amount of reagentmetal added is sufficient to reduce silica and Zinc sulfide inclusionsin the untreated alloy .matrix to an average of not more than one silicaand ten zinc sulfide inclusions per square millimeter of metalcross-sectional surface.

11. A leaded free-cutting brass of improved machineability that has beentreated to reduce inclusions that are commonly present in ordinaryfree-cutting brass and harmful to tool life, said treated brasscontaining as an inclusion-reducing reagent metal a small but effectiveretained amount, sufficient to effect substantially complete eliminationof inclusions commonly present in untreated free-cutting, of a memberselected from the group consisting of sodium, lanthanum, cerium, andmixtures thereof.

12. A leaded free-cutting brass of improved machineability that has beentreated to reduce inclusions that are commonly present in ordinaryfree-cutting 'brassand harmful to tool life, said-treated'brass'containing as an inclusion-reducing reagent metal a small buteffective retained amount of sodium, sufficient to effectsubstanmachineability by changing conditions harmful to tool life byeflfecting substantially complete elimination of inclusions commonlypresent in untreated free-cutting brass, said metal being selected fromthe group consisting of sodium, lanthanum, cerium, and mixtures thereof.

14. A method of treating a free-cutting leaded brass to create a productthat is characterized by substantial freedom from inclusions that areCommonly present in ordinary free-cutting brass and harmful to toollife, and that is further characterized by improved machineability,comprising introducing into a melt thereof an amount of sodiumsufiicient to provide in the brass as cast a small retained amount ofsodium, that is sufiicient to effect substantially complete eliminationof inclusions commonly present in untreated free-cutting brass.

15. A method of treating a free-cutting leaded brass having a nominalanalysis of from about 60% to about 65% copper, about 0.5% to about 3.7%lead, and the remainder zinc except for incidental impurities, in orderto improve the machineability thereof, that comprises introducing into amelt thereof an amount of a reagent metal sufficient to reduce theincidence of inclusions normally present in such alloys and to improvemachineability, and to provide in the brass as cast a small retainedamount of the reagent metal, suificient to effect substantially completeelimination of inclusions commonly present in untreated free-cuttingbrass, Where the reagent metal is selected from the group consisting ofsodium, lanthanum, cerium, and mixtures thereof.

References Cited by the Examiner UNITED STATES PATENTS 1,937,934 12/1933Zimmerli.

2,173,254 9/1939 Hensel et al.

2,795,501 6/1957 Kelly 75l53 XR 2,879,159 3/1959 Bolkcom et a1.

2,970,248 1/1961 Sahagun 75-153 XR DAVID L. RECK, Primary Examiner.

7. THE METHOD OF TREATING LEADED BRASS TO REDUCE SILICA AND ZINC SULFIDEINCLUSIONS COMMONLY PRESENT IN THE UNTREATED METAL IN ORDER TO IMPROVETHE MACHINABILITY THEREOF, WHICH COMPRISES INTRODUCING INTO THE BRASSMELT AT LEAST ONE REAGENT METAL SELECTED FROM THE GROUP CONSISTING OFSODIUM, LANTHANUM AND CERIUM, IN AMOUNT SUFFICIENT TO PROVIDE IN THECAST ALLOY AN EFFECTIVE AMOUNT SUFFICIENT TO EFFECT SUBSTANTIALLYCOMPLETE ELIMINTION OF SUCH INCLUSIONS, UP TO 0.30% BY WEIGHT OF SAIDREAGENT METAL.